Discuss whether we want to use POP3 by default if persistence is enabled
Before replacing TorBirdy, we meant to default to POP3 instead of IMAP if Thunderbird persistence is enabled, by using the
This doesn't seem to have worked, see #17219#note-16.
We might still want to support this, but that would mean we would have to create another Thunderbird patch. We should discuss whether that's worth it.